1. Field of the Invention
The present invention relates to manipulator apparatus, and more particularly to manipulator apparatus for supporting and orienting the test head of an automatic test system.
2. Description of Related Art
Manipulators are intended to enable the position in elevation, azimuth, and orientation of a heavy test head to be adjusted manually so that the test head can be engaged accurately with and docked to a device handler, which is a device that feeds the test head with electronic circuits to be tested.
Electronic test heads are heavy assemblies comprising a structure supporting and protecting a large number of driver and comparator circuits which are connected to an automatic test equipment by connection cables. Each integrated circuit to be tested is successively positioned on the test head from a device handler to which the head is docked. In general, such heads are organized in the form of approximately rectangular cases which can be carried via two stub axles fixed to two opposite sides of the case in a balanced condition since the weight of the head is distributed symmetrically about these stub axles.
Other electronic test heads which will be called here asymmetrical heads have a cylindrical case with a radially extending rigid arm, containing electrical connection cables and cooling hoses.
Known manipulator apparatus, such as the one described in U.S. Pat. No. 4,527,942 (Smith), comprise a U-shaped support member or cradle which is designed to support a symmetrical test head in a balanced weight condition such that the head can be moved manually to any position in which it can be docked to a device handler.
Such manipulators are not suitable for handling asymmetrical test heads. First, stub axles disposed on opposite sides of the cylindrical case of an asymmetrical head would not support the head in a balanced condition. Secondly, a rotation of 180 degrees would not be possible with a U-shaped support engaging such stub axles due to the length of the radially extending arm which contains the connecting cables. In other words the known manipulator apparatuses are not suitable for handling asymmetrical test heads of the type described above with the required number of degrees of freedom.
An important requirement is to be able to rotate the test head by 180 degrees to have access to the lower side thereof. Another important requirement is to be able to rotate the head manually about two substantially perpendicular axes. A third important requirement is to install the test head on the manipulator or to remove it therefrom easily and without disconnecting the head from the automatic test equipment. The above requirements cannot be obtained when known manipulators are used with asymmetrical test heads.